Infinite-axis telescope
Encyclopedia
An infinite-axis telescope is a telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 that can move freely in all directions. Such telescopes can be mechanically simple hand-guided versions with the mounting
Telescope mount
A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument...

 serving only to carry the weight of the telescope although there are equatorial
Equatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...

 versions.

Types

An example of this type of telescope was the late 17th century "Air" or "Aerial telescope
Aerial telescope
An aerial telescope is a type of very-long-focal-length refracting telescope built in the second half of the 17th century that did not use a tube. Instead, the objective was mounted on a pole, tree, tower, building or other structure on a swivel ball-joint. The observer stood on the ground and held...

", which was a very long focal length
Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...

 refracting telescope
Refracting telescope
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image . The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses...

 that did not use a tube. In these telescopes a hand held eyepiece
Eyepiece
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings...

 and an objective mounted on a ball joint were connected by a string; the observer kept the string tight and moved the eyepiece to aim the telescope.

Another example of an infinite-axis telescope is a ball-in-cup mounted telescope, also called a spherical-mounted telescope. The first Newtonian telescope
Newtonian telescope
The Newtonian telescope is a type of reflecting telescope invented by the British scientist Sir Isaac Newton , using a concave primary mirror and a flat diagonal secondary mirror. Newton’s first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope...

 was mounted in this way; the ball was held in place by wrought iron springs. Another type uses a bowling balls as a mount axis. There are modern commercial and amateur
Amateur telescope making
Amateur telescope making is the activity of building telescopes as a hobby, as opposed to being a paid professional. Amateur telescope makers build their instruments for personal enjoyment of a technical challenge, as a way to obtain an inexpensive or personally customized telescope, or as a...

 mount designs for Newtonian telescopes that have the "ball" built into the base of the optical tube assembly. These mounts have the advantage of being mechanically simple and allow the observer to rotate the eyepiece to any side of the telescope for easier viewing. Some types have even been adapted for equatorial tracking by motorizing one of the bearing surfaces to turn the ball at the rate of one revolution per day. This rotates the telescope's ball exactly opposite the rotation of the Earth, thus keeping the telescope stationary with respect to the stars.

Small, hand-held (richest-field) telescopes may also qualify as infinite-axis telescopes.

An advantage of infinite-axis telescopes is that there is no "dead-zone" where one axis must move infinitely fast in order to track the stars, as is the case with alt-azimuth mounts.

Further reading

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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